Those stocking meat slaughtered according to Islamic law include Waitrose, Marks & Spencer, Sainsbury’s, Tesco, Somerfield and the Co-op.

And a Mail on Sunday investigation has found that fast-food chains including Domino’s Pizza, Pizza Hut, KFC, ­Nando’s and Subway are also using halal meat without ­telling customers.

But the UK’s second-biggest supermarket, Asda, has refused to confirm or deny whether it sells halal meat.

The Mail on Sunday contacted Asda on Tuesday, but by yesterday it had failed to answer any of our questions.

Initially, Waitrose, Sainsbury’s and Tesco were reluctant to admit they sold halal meat. But later they confessed to selling Islamically slaughtered lamb. Tesco also admitted selling some halal chicken without labelling it as such.

Most lamb imported from New Zealand by British supermarkets has been slaughtered according to Muslim law, but this is not mentioned on packaging. Some lamb from British abattoirs is also halal.

Last night, Agriculture Minister Jim Paice said: ‘People should know what they’re buying in the shops or when they’re eating out and I will be discussing with the food industry the role labelling can play in giving consumers a choice.’

The supermarkets and fast-food outlets said they did not feel the need to tell customers that meat is halal because the slaughter conformed to Western standards, with animals stunned before being killed.

But the RSPCA has raised concerns about the way chicken is killed in Islamic abattoirs because the birds are stunned with a weaker electric current, which does not guarantee unconsciousness during slaughter.

Our enquiries have found that ­Subway uses some Islamically slaughtered chicken that has not been stunned.

Our enquiries have found that ­Subway uses some Islamically slaughtered chicken that has not been stunned.

Non-Muslim religious leaders say that Christians, Hindus or Sikhs may find it offensive to eat meat slaughtered according to Islamic ritual. Jews are unlikely to be exposed to such meat because they eat kosher, or animals slaughtered according to Jewish law.

Last week The Mail on Sunday revealed how halal food was being served to unsuspecting people in hospitals, schools and pubs across the UK.

The country’s biggest hotel and restaurant group, Whitbread– which owns the Beefeater and Brewers Fayre chains – was also selling halal food, as were well-known sporting venues such as Ascot, Twicken­ham and Wembley.

Under Islamic law, an animal must be slaughtered by having its throat cut while it is conscious.

All its blood must drain out, otherwise Muslims regard it as impure. The person carrying out the killing has to recite an Arabic verse at the time.brings the practice in line with Western methods.

All Islamically slaughtered lamb and chicken sold in British supermarkets is stunned before being killed, but is not labelled as halal. Moderate Islamic groups allow animals to be stunned before slaughter, which brings the practice in line with Western methods.

Inayat Bunglawala, the chair of Muslims4UK, said: ‘Supermarkets should not be afraid of labelling their products as halal. Halal meat tastes just the same as non-halal meat.’

But Mike Judge, from the campaign group the Christian Institute, said: ‘The idea of having Islamic ritual said over meat would be objectionable to some Christians. I would find it objectionable, so it should be labelled as halal.’

Initially, Tesco and Waitrose were reluctant to admit they sold any halal meat. Tesco said in a statement: ‘It is not the case that all the meat we sell is halal or that our suppliers only offer halal meat.’

But when quizzed further, a spokesman said: ‘All our New Zealand lamb is halal-slaughtered, as is 35 per cent of our UK lamb. Less than five per cent of our chicken is halal.’

A Waitrose spokeswoman said in her first statement: ‘I can confirm that Waitrose does not sell any halal meat.’

But a day later, another spokes­woman said: ‘You mentioned the [Islamic] prayer said at the point of slaughter. This applies to all our lamb but not to beef or poultry.’

M&S said in its first statement: ‘No meat sourced by M&S from the UK is halal.’ When asked about lamb, a spokeswoman said: ‘Our New Zealand lamb is halal-slaughtered but pre-stunned.’

A Sainsbury’s spokesman said: ‘The abattoirs that supply us with lamb are licensed by the Muslim authorities and a prayer is said when the ­animals are killed.’

Sandwich chain Subway admitted that up to five per cent of its chicken is Islam­ically slaughtered without being stunned.

Subway said in a statement: ‘By mid-November there will be no halal meat in our non-halal stores. The meat served in halal Subway stores is not stunned before slaughter.’

Domino’s Pizza said it had served Islamically slaughtered chicken in most of its 580 outlets for ten years.

I kill 45 chickes a minute and all get an Islamic prayer

The Muslim slaughterman murmurs the Islamic verse as thousands of chickens whir towards him on a conveyor belt hung from the ceiling.

Masood Akhtar grabs hold of one chicken’s head with his left hand and, with his right, draws his knife across its neck.

The slaughterman barely has time to say ‘Bismillah Allah-hu-Akbar’ (meaning ‘In the name of Allah, who is the greatest’) before the next bird is upon him.

It appears a long way from the ritualised slaughter that many would imagine produces halal chicken. Mr Akhtar is not dressed in robes but in a hair-net and a yellow blood-spattered jacket.

And far from a spiritual ceremony, the process is clinical and robotic – Mr Akhtar claims to kill 45 birds every minute and 40,000 in a week.

The procedure appears to follow Sharia law, which states that the bird must be killed alive by a Muslim man who recites the set verse as he cuts its throat.

At the Paul Flatman Ltd poultry processing plant outside Colchester in Essex where Mr Akhtar works, the chickens are stunned by dipping them in electrified water before they are killed.

‘The charge stuns the birds for around two minutes – it’s like a general anaesthetic,’ explained factory manager Tim Lane.

‘It’s crucial not to kill the bird because then, it wouldn’t be halal, so we adjust the charge depending on the chicken’s size. We are very careful to get the balance right.

‘Some of the other bigger poultry factories who are supplying the supermarkets claim the chicken they produce is halal – but it’s not really.

‘Instead of using a Muslim man as the killer, they use an automatic circular saw and a tape recorder to play the prayer.

‘They can’t do it properly because of the sheer volume of chickens they have to kill to meet demand. Some of the factories are doing one million birds a week.’

Mr Akhtar, 29, became a slaughterman at the age of 18 after a few months’ training.

‘When I arrived I wanted to be a killer,’ he recalled. ‘On my first day in training, three out of ten birds I killed were not cut properly through both neck arteries – this meant they were not halal.

‘But after three months
of practice I was perfect – every bird was killed in true halal style.’

The Paul Flatman plant opened in 1961 slaughtering chickens in the normal way, but in 1977, as demand from halal wholesalers increased, Mr Flatman switched his entire production to halal.

He says he has never found it hard to recruit Muslim slaughtermen. ‘It’s usually just through word of mouth in the Muslim community – it’s not hard to find volunteers.’

I am a qualified meat inspector and have lost count of the days and weeks I’ve spent in slaughterhouses. I’ve never liked the ritual way of killing – I don’t believe it is humane.

I don’t know any slaughterman who likes it either. But we accept it because it is the law – even though the law has been fudged because the issue is too sensitive for the Government and the EU (which now makes the rules) to take on.

A spokeswoman said: ‘The majority of our chicken is halal slaughtered, but it is all stunned prior to slaughter.’

Pizza Hut and KFC, through their PR firm Freud Com­munications, said: ‘We use a number of international suppliers, some of whom provide halal chicken as standard practice.

‘Importantly, all of the chicken we source, halal or otherwise, is stunned before slaughter.’

Nando’s said: ‘All of our chickens are stunned first. A small proportion of all the chicken sold in our restaurants is halal.’

They HAVE to tell us what we’re buying

Analysis by Richard North

Even though I’ve seen it done thousands of times, you never really get used to watching animals being killed. But as long as we eat meat, it has to be done. And it is our duty as a society to ensure that the procedure is carried out humanely and with as much dignity as possible.

Society also has to respect religious freedom and rituals, and I don’t have a problem with that. I am, however, uneasy that the laws that require humane killing of animals for meat – particularly that they must be rendered insensible before being slaughtered – do not apply to Jews for their kosher meat and Muslims for halal foods.

It is a fudge we have all lived with, however uneasily, for years, feeling safe in the knowledge that this is very much a niche market. Only last week the Office for National Statistics reported that just four per cent of the British population was Muslim.

Surely, if you want halal or kosher meat, you go to a specialist butcher and everybody else can be confident their meat is produced to more humane standards?

Well, actually, no. That choice has been scandalously taken away from us. Not only are we deliberately not informed if our meat is produced according to religious ritual, many retailers do not even know.

And there is only one real reason: profit. The reality of modern meat production, both here and abroad, is that most animals are killed in vast, modern slaughterhouses.

Once there were small, specialist kosher and halal producers, but now the trade has been taken over by industrial concerns. To cover the increasing demand for halal meat, these corporate slaughterhouses have either had to introduce halal methods or buy in halal meat from specialist butchers.

The choice is either to introduce a separate production line or to take the cost-cutting option of having just one production line. But in this one-size-fits-all world, it’s not the most humane and dignified method of slaughter – the one enshrined in British and EU law – that wins out.

No, the ‘one-size’ is the less humane method of killing tailored to the religious demands of just four per cent of the population. Since it is not illegal to palm off halal meat on non-Muslims, that is being done on a massive scale. And there is nothing the Government or the EU can or will do about it.

The UK has draconian regulation, far more rigorous than in the rest of Europe. But this was supported by the large slaughterhouses which thought that closing down smaller competition would increase their market share and profit margins. In this country, the combined pressure of regulation and the greed of commercial producers have ensured local butchers are now rare, and local slaughterhouses even rarer. And it is the massive factory abattoir, hidden from sight, that perpetrate these practices.

Thus, commercial greed has found a way of circumventing a law that we, in our ignorance, expect to be obeyed and that we have a right to see obeyed.

We do not expect commercial interests to prevail, on a technicality, over something that many campaigned for – the humane slaughter of our animals.

This is not only commercially wrong, morally it is a disgrace.

* Author and journalist Dr Richard North is a qualified meat inspector and former technical adviser to the Small Abattoirs Association.